The invention relates to an apparatus for reading a disk-shaped record carrier on which video information is recorded in accordance with an optically detectable structure in substantially parallel tracks. Such an apparatus comprises an optical read unit comprising a read detector for detecting the information contained in a read beam after co-operation with a record carrier and a deflection element which cooperates with the read beam to vary the radial scanning position on the record carrier, and, in response to a control signal, is movable in two opposite directions relative to a center position. The apparatus further comprises a drive means for radially moving the optical read unit and a servo control loop for controlling the radial scanning position on the record carrier. The servo control loop includes the deflection element and a measuring detector for measuring the radial deviation of the scanning position relative to desired track and for deriving therefrom the control signal for the deflection element. The servo control loop also has switching means for rendering the loop inoperative during controlled time intervals and an actuating device for causing the deflection element to move at least towards the center position during said time intervals.
Such apparatus is disclosed in U.S. Pat. No. 4,330,880. The apparatus disclosed in said Patent enables a desired program section on the record carrier to be located rapidly while maintaining at least a reasonable picture reproduction during this search operation.
In addition to the visual search for a desired program section, a desired program section on such record carriers can also be located automatically. The video pictures recorded on such a record carrier generally have an individual picture number, which is inserted as a digital signal in the vertical flyback period of the video signal. This means that by keying-in a picture number, an automatic-search operation can be started, a control signal for the drive means of the optical read unit being obtained by comparing the number of the picture being read instantaneously with the desired picture number, so that said read unit can be moved very rapidly to the desired radial position to read the desired video picture. During this search operation, when very rapid movements of the optical read element may occur, it is no longer important to maintain the picture reproduction. However, during the search operation it is important that information about the position of the scanning spot on the record carrier is available.